The present invention relates to shock absorbers generating a damping force by utilizing the fluid pressure.
Shock absorbers attached to suspension systems of automobiles or other vehicles generally have the following structure. A piston connected to a piston rod is slidably fitted in a cylinder having a fluid sealed therein. A stroke of the piston rod causes sliding movement of the piston in the cylinder, which, in turn, induces a flow of fluid. The fluid flow is controlled by a damping force control mechanism comprising an orifice, a disk valve, etc., thereby generating a damping force.
A hydraulic shock absorber disclosed in Japanese Patent Application Publication No. 2006-10069, for example, has a back pressure chamber (pilot chamber) formed at the back of a main disk valve constituting a damping force generating mechanism. A part of the fluid flow is introduced into the back pressure chamber, and the pressure in the back pressure chamber is applied to the main disk valve in the direction for closing the valve. The pressure in the back pressure chamber is adjusted by a pilot valve, thereby controlling the valve opening of the main disk valve. This technique makes it possible to increase the degree of freedom for adjusting damping force characteristics.
In the hydraulic shock absorber disclosed in Japanese Patent Application Publication No. 2006-10069, an annular oil seal (elastic seal member) is fixed to the rear surface of the main disk valve. The oil seal is slidably and gas-tightly fitted into a circular cylindrical portion of a valve member in the shape of a circular cylinder, one end of which is closed, thereby forming a back pressure chamber. This structure needs to increase slidability and sealability between the cylindrical portion of the valve member and the oil seal in order to allow the main disk valve to open and close smoothly and to thereby obtain stable damping force characteristics. In this regard, if such a structure is adopted that an inner peripheral portion of the main disk valve is secured by being axially clamped (see FIGS. 4 and 10 in Japanese Patent Application Publication No. 2006-10069), it is necessary to increase the coaxiality between the oil seal, the main disk valve and the valve member in order to increase the slidability and sealability between the cylindrical portion of the valve member and the oil seal.